1. Field of Invention
This invention relates generally to a digital pulse modulator. More particularly, this invention is directed to methods and systems that use multiple pulse width and position modulation (PWPM) circuits driven from the same system clock and video data to provide multiple video pulses per clock period.
2. Description of Related Art
In a system that uses one or more beams to record information, for example, on a photoreceptor, a digital pulse forming circuit may be used to control the one or more beams. Each beam may vary in intensity and duration according to the pulses used to control that beam.
One or more laser beams may be used in a printer or photocopier, for example, for discharging negative image areas on a photoreceptor. The latent electrostatic image formed on the photoreceptor by the one or more beams attracts developing toner in proportion to the latent image charge level in order to develop the image.
As another example, a cathode ray tube uses an electron beam to scan a phosphorus screen. The electron beam may be varied in intensity and duration to accurately display information on the phosphorous screen.
In both examples, a pulse forming circuit may be used to generate pulses to control the intensity and operation duration of the respective beams. In a high speed image forming system, the reset time of a pulse forming circuit is the time needed for the pulse forming circuit to reset to an initial state before a new pulse can be generated. Thus, the speed of a pulse forming circuit is limited by the amount of time it takes the circuit to form a pulse and reset to its initial state. U.S. Pat. Nos. 4,965,675 to Duke et al., 4,905,023 to Suzuji, 4,375,065 to Ohara, and 4,347,523 to Ohara each describe pulse forming circuits, systems and/or methods.
U.S. Pat. No. 5,184,226 to Cianciosi, incorporated herein by reference in its entirety, describes a digital electronics system that generates pulses from a series of data words. The digital electronics system includes lookup tables to translate each data word into a pulse attribute word. Each pulse attribute word includes information to controllably form a corresponding pulse. The digital electronics system also includes one or more multiplexers that split the series of pulse attribute words, generated from the series of data words, into two channels.
The digital electronics system of the 226 patent further includes pulse forming circuits for each channel. Each pulse forming circuit receives the pulse attribute word from the corresponding channel. Each pulse forming circuit forms a pulse based on the received pulse attribute word. The digital electronics system of the 226 patent additionally includes control circuits that generate and output the pulses to the beam emitting devices. In particular, in the digital electronics system described in the 226 patent, a first pulse from a first pulse forming circuit is generated while a second pulse from a second pulse forming circuit is being formed.